Lithographic plates



iinited States Patent "50- LITHOGRAPHIC PLATES' Charles F. Geese, Old Greenwich, C-onn., assignor, by mesne assignments, to Chrome Steel Plate Corporation No Drawing. Application May 3, 1954 Serial No. 427,383

3 Claims. (Cl. 101-149.2)

that printing according to the principles of lithography is particularly desirable and may be quite versatile, still the advance and furtherance of the lithographic art has not kept apace with other forms of printing. This relative decline or slackening in the advance of lithography has been attributed to several causes, prominent among which have been the unreliability of the less expensive and common zinc and aluminum lithographic plates, their inability to print long press runs without loss of graphic detail and the high cost of the more reliable, long run plates such as chromium plated copper plates.

I have discovered that lithographic printing of superior quality and excellent detail may be attained according to the present invention, while still preserving the attractive low cost features of common Zinc plates and yet avoiding their limitations and disadvantages. In general, these features are disclosed in my co-pending application identified above.

Before discussing the features of the present invention further, it is to be noted that the subsequent description of specific details of the invention is generally intended to be illustrative of the invention and not limiting thereof, the invention being defined with more formal particularity in the appended claims.

The invention may perhaps best be described and illustrated by recounting chronologically the sequence of treatment steps I have employed and am using in preparing commercially acceptable lithographic plates which have, in several instances made overa million impressions per plate and are capable of considerably greater service. It is to be noted that the maximum runs heretofore made have not been limited by the plate used but only by the number of impressions ordered by the customer.

In a preferred procedure I first take a flat 58" x 77" 24 gauge bright finished cold rolled steel plate, as for example a low S.A.E. 1000 series plate presently available from Inland Steel Company, Chicago, Illinois, and, after removing any rust preventives therefrom, I clean the base plate by scrubbing it with pumice and dilute hydrochloric acid. Thereafter, unless the plate is to be subjected promptly to the next treating step, I coat the cleaned and polished side of the plate with gum arabic or an equivalent inert protective coating to avoid any oxidation or corrosion of the polished surfaces.

Next I prepare the plate for the chromium plating bath by washing 01f the gum or similar intermediate protaining gum arabic or 239 273 Patented Oct. 6, 9

Current Voltage Time 5,000 amps- Current on 5 000 amps Current otf 6,000 amps Current off 6,500 amps 1 minute. 10 seconds. 1 minute. 10 seconds. 40 seconds. 10 seconds. '1 minute.

6 (approx.)

6 (approx.) 6 plus..

hiapprox.) "I:

Although variationsin the'chromium plating cycle may be made, I find that the cycle specified above is preferable, yielding a dull finish chromiumplating of about 35 ten-thousandths of an inch thickness. Optionally, one,

may also initially reverse the current for about half a minute to a minute and a half so that the plate is first used as a cathode. It will beobserved that in the preferred plating cyclethe current density lies between 1 and 1.5 amperes per square inch. I

Upon removal from the chrome plating bath, the plate is Washed with water; optionally it may be coated with gum arabic or an equivalent if significant intermediate storage is contemplated. Otherwise, the plate while still moist is placed in a conventional horizontal centrifugal Whirler and there coated with a standard light sensitive resist or coating, such as a conventional bichromated gum. I prefer to use a-deep etch resist material conglue with ammonium or potassium bichromate. V v

Thereupon, the dried plate is in condition to receive the image. Typically the image to be printed will be placed on the plate byusing a photographic positive which is exposed to light according to conventional practiceto form light hardened areas and soft areas which are the image areas. Then the unexposed or soft resist material is washed away with a standard developer such as a solution of calcium chloride and Zinc chloride. After the soft resist has been removed, the plate is washed with ethyl alcohol or the like, dried and then staged with lacquer or tape or perhaps both, if needed to mask any defects. Y

After staging, the plate is etched with a standard chromium etching solution such as a solution of hydrochloric acid and calcium chloride, in order to remove the chromium and expose the steel which had been beneath the soft resist material. The etching is carried on for about four to five minutes, at which time the bright steel image.

areas are readily apparent to the View.

Thereupon the etched plate is thoroughly rinsed with concentrated ethyl alcohol, an ethylene glycol ether (such as those sold under the proprietary name of Cellosolve by Carbide and Carbon Chemicals Company, New York, New York) or the liketo remove any residual etching solution.

The subsequent stage of treatment of the etched plate involves a cleaning operation with a mild abrasive mixturethe mixture being one which does not seriously aifect the light hardened resist material over the chromium plate and thus avoids scratching of the chromium while still mildly abrading the steel image without permitting the build-up of flaking or non-printing oxides, non-printing complex films or non-printing addition compounds.

1 Ounces Ammonium chloride 2 Water 6 Ethyl alcohol 176 Ferric chloride 2 Cupric chloride 1 To this solution there is admixed ounces of very fine pumice powder and 2 ounces of bismuth oxychloride or subchloride. This mixture is then rubbed briskly over the plate for about 2 to 2% minutes. After this treatment, I wash 01f any residual staging lacquer with a suitable solvent, such as ethyl alcohol. It will be appreciated by those skilled in the art, that variations in the concentration of the sensitizing mixture and the cleaning time may be made, depending .upon the sizeof the plate treated and the skill and characteristics of those persons applying the mixture thereto.

Next the hard resist is washed off the plate with a good detergent solution. I have had good results using a solution of Oakite No. 27 maintained at 160 F., although even household detergents such as Tide (Procter & Gamble, Cincinnati, Ohio) may also be used. The plate is next flushed with water and then the chromium on the plate is passivated or rendered repellent to ink by applying thereto a phosphoric acid material, for example, such as may be obtained from Merck & Company, Rahway, New Jersey, or Oakite No. 36 from Oakite Company, New York, New York.

After this treatment, surplus passivating agent is removed so that the plate is just damp. While the plate is in this condition, I apply a standard protective lithographers varnish to the plate to facilitate the later application of rub-up ink. For example, I recommend the use of a varnish such as that sold by McKinley Litho Supply Co. of Cincinnati, Ohio, under the trade-name No Wok." This varnish is believed to be essentially comprised of furfiuryl alcohol and asphalt, thinned with turpentine. I then add a small amount of the inhibited phosphoric acid (Oakite No. 36) with a standard rub-up ink and apply this to the plate to protect the exposed steel image areas. The plate is then washed with water and a protective coating of gum arabic applied so that the plate may be inspected carefully and corrections made, if needed. Then the plate is washed with solvent thinned asphaltum to remove any dried or hardened ink on the image, the asphaltum then preferentially protecting the steel image. The plate isthen rmdy for the press.

It is my present belief that the combination of a mild etcha mild abrasivea group V metal salt, particuquence of treating steps needed to form a chromiumsteel lithographic printing plate, receptive to ink in the steel printing surfaces and yet capable of fine printing detail and long durability.

Having now particularly described my invention, what I claim is:

1. A lithographic printing plate having image areas and non-image areas which comprises a low-carbon nonstainless steel plate, the non-image areas of said plate containing an overlying coating of dull hydrophilic inkrepellant chromium, the image areas of said plate being recessed relative to said chromium coating, said image areas being in a sensitized hydrophobic ink-receptive larly a halide thereof is especially etficacious in the sestate and being comprised of the reaction product of said steel with a solution of ammonium chloride, ferric chloride, cupric chloride and bismuth oxychloride.

2. The method of sensitizing the image areas of a low carbon non-stainless steel lithographic plate having image areas and non-image areas, the non-image areas of said plate containing an overlying coating of dull hydrophilic ink repellant chromium, the image areas of said plate being recessed relative to said chromium coating, which method comprises applying to the steel image areas of the plate a solution of ammonium chloride, ferric chloride, cupric chloride and bismuth chloride.

3. The method as in claim 2'in which said solution also contains pumice.

References Cited in the file of this patent UNITED STATES PATENTS 758,599 Sachers Apr. 26, 1904 773,368 Bower Oct. 25, 1904 1,042,827 Schumacher Oct. 29, 1912 1,069,856 Cornwall Aug. 12, 1913 1,163,166 Niemeyer Dec. 7, 1915 2,042,003 Huebner May 26, 1936 2,427,107 Petren et al Oct. 14, 1947 2,437,005 Schwarz Mar. 2, 1948 2,599,914 Hartsuch et al. June 10, 1952 2,623,847 Gilbert et a1. Dec. 30, 1952 2,676,886 Barburite Apr. 27, 1954 2,686,756 Stareck et a1. M Aug. 17, 1954 2,703,295 Kantrowitz et al Mar. 1, 1955 2,750,881 Geese June 19, 1956 FOREIGN PATENTS 330,674 Great Britain June 19, 1930 Great Britain Sept. 14, 1949 OTHER REFERENCES Tory: Photography, published 1953 by Graphic Arts Monthly, Chicago, Only page made of record. 

1. A LITHOGRAPHIC PRINTING PLATE HAVING IMAGE AREAS AND NON-IMAGE AREAS WHICH COMPRISES A LOW-CARBON NONSTAINLESS STEEL PLATE, THE NON-IMAGE AREAS OF SAID PLATE CONTAINING AN OVERLYING COATING OF DULL HYDROPHILIC INKREPELLENT CHROMIUM, THE IMAGE AREAS OF SAID PLATE BEING RECESSED RELATIVE TO SAID CHROMIUM COATING, SAID IMAGE AREAS BEING IN A SENSITIZED HYDROPHOBIC INK-RECPTIVE STATE AND BEING COMPRISED OF THE REACTION PRODUCT OF SAID STEEL WITH A SOLUTION OF AMMONIUM CHLORIDE, FERRIC CHLORIDE, CURPIC CHLORIDE AND BISMUTH OXYCHLORIDE. 